Enzymic hydrolyses and oxidation processes occur naturally both in solid and liquid media, and generally give a range of products. The crude mixture may be unpleasant, but individual components may be desirable. Therefore, it is known to perform the processes artificially for oxidation of naturally occurring materials.
Commercial aerobic enzymic processes are normally carried out in solution. This has to be relatively dilute to allow oxygen to be distributed easily throughout the mixture, as otherwise aeration becomes difficult. Thus, the biotransformation solution must be a dilute solution and the yields resulting from such a dilute solution are relatively low.
Solid state processes are also known. The solid phase can be the substrate that is to be converted (e.g., malting of barley grains) or can be a support for the aqueous medium in which the oxidation occurs. In Process Biochemistry, July 1966, J. Meyrath describes production of amylolytic enzymes by growth of various molds which produce such enzymes on bran and on vermiculite to obtain a yield of the amylase enzyme. In addition, Oriol et al., in the Journal of Fermentation Technology, volume 66, number 1, pages 57 to 62, describe how Aspergillus niger fungus was grown on a solid support of sugar cane bagasse.
The solid state process described by Meyrath is for the production of the enzyme itself. However, it is also known to use the enzymes formed to obtain the biotransformation products that they produce. Another solid state reaction is discussed in Advances in Applied Microbiology, volume 28, pages 201 to 237, for the production of citric acid on inert materials. Sawdust and sugar-free sugar cane bagasse were used as the growth support, and this was impregnated with sugar solution. The inert materials were inoculated with mold culture, and citric acid was produced. Other growth supports mentioned are rice hulls and wheat bran.
It is known that natural atmospheric oxidation of fats and oils produces a crude, unpleasant product (e.g., rancidity), but that some components of the product can be useful.
In Phytochemistry (1984) volume 23, number 12, pages 2847 to 2849, Kinderlerer describes natural oxidation of coconut due to the action of molds natural to the coconut as giving a series of aliphatic methyl ketones and secondary alcohols. In Phytochemistry (1987) volume 26, number 5, pages 1417 to 1420, she described their production in a liquid medium, following growth of Aspergillus ruber and A.repens fungi with coconut oil as the sole carbon source. However, low yields were obtained.
It is also known to use milk and milk compounds as a growth medium for biotransformation reactions. For example, ketones have been produced by biotransformation processes on milk and milk compounds. In U.S. Pat. No. 3,100,153, a process is described wherein pasteurized homogenized milk containing milk fat is fermented under submerged aerobic conditions using Penicillium roqueforti to produce ketones, and in U.S. Pat. No. 3,720,520, ketones giving a blue cheese flavor are produced by growing Penicillium roqueforti with aeration in an aqueous medium of sodium caseinate and fat.
Such blue cheese flavors are also described in pages 285-287 of volume 40 (1975) of the Journal of Food Science, where R. Jolly and F. V. Kosikowski report studies of biotransformation of coconut fat and butter fat with whey powder, carried out in an aqueous medium, again using Penicillium roqueforti.
U.S. Pat. No. 4,769,243 describes the preparation of green aroma compounds by reaction of at least one unsaturated fatty acid (which may be produced in situ from fat and lipase) with enzymes from soy beans. An aqueous solution of water and ground germinating soy beans is mixed with linseed oil, and the mixture is allowed to react while stirring rapidly. Air or oxygen is supplied to the mixture throughout the reaction. The resulting reaction is due to the enzymes present in the germinating soy bean. This type of liquid process must be stirred rapidly to ensure that the mixture remains substantially homogeneous. In addition, it is difficult to provide oxygen throughout the whole reaction mixture, and so liquid mixtures as described above must be relatively dilute and require some form of intermixing. If the amount of water is reduced, the fat tends to form a very viscous continuous phase between the particles of ground bean, and this will prevent adequate oxidation.
It would be desirable to devise a process of enzymically oxidizing fats and/or fatty acids and that can be performed easily and to give high yields of the desired products. It would also be desirable to provide novel apparatus suitable for such processes.